Projection apparatuses and associated methods

CROSS REFERENCE TO RELATED APPLICATIONS

0001This application is a Divisional application that claims priority to co-pending U.S. Utility patent application entitled, “Projection Apparatuses and Associated Methods”, having Ser. No. 13/175,039, filed Jul. 1, 2011, which is a Continuation-in-Part application that claims priority to U.S. Utility patent application entitled, “Projection Screen and Method of Construction”, (now U.S. Pat. No. 8,149,509), which claims priority to U.S. Provisional Patent Application entitled, “Projection Screen and Method of Construction”, having Ser. No. 61/051,397, filed May 8, 2008, each of which is entirely incorporated herein by reference.

BACKGROUND

00021. Technical Field

0003The invention relates to a projection screen and method. More particularly, but not exclusively, it relates to a projection screen retained by a retention member, and a method for constructing such a screen.

00042. Description of the Related Art

0005The projection of an image upon a partially reflective and partially transparent screen such that it is observable by a viewer positioned in front of the screen is known as a “Pepper's ghost” arrangement from fairground shows.

0006Pepper's ghost projections have been used in publicity and promotional displays where a presenter resides behind an inclined, partially reflective partially transparent screen, typically a tensioned foil, onto which an image of, for example, a motor vehicle is projected, via at least one reflective surface, see for example EP 0799436. The location of the presenter behind the projected image has a number of inherent advantages over systems where the presenter stands in front of a screen, not least of which is that the presenter does not obscure the projected image when walking across the projected image. Additionally, the use of an inclined screen results in a viewer of the image perceiving the image as having depth rather than merely being a two dimensional image, for example where a motor vehicle is seen to rotate upon a turntable.

0007However, current image projection apparatus' do have a number of problems associated with them, for example, mounting of the foil can prove difficult which in turn leads to uneven tensioning of the foil and wrinkles upon the foil, that impair the viewed quality of the image. It is well known in the art that wrinkles inevitably form in a screen over a period of time with a resultant distortion of the projected image. Indeed, a wrinkle-free screen may be assembled in the evening, and by the following morning, wrinkles will have appeared as a result of the screen settling. Furthermore a change in conditions, such as humidity or temperature, can cause wrinkles to form in the space of minutes. In practice, it has been found that due to the thickness of large sized foils (e.g. 4 meter length foils are 88-110 microns thick and 5.5 meter length foils are approximately 50 microns thick) settling of the screen often only occurs after approximately 48 hours. When wrinkles appear, it is necessary to retension the screen and in particular the levels of tension required exceed those achievable by user force alone.

0008WO 2005/096095 (Musion Systems Limited) provides an apparatus capable of providing even tensioning of the foil by application of pressure at a plurality of positions along at least one edge of the screen. This apparatus requires placing an edge of the screen between jaws and passing a bolt through the screen. A nut is then threaded onto the bolt and tightened to hold the screen between the jaws. Tensioning is provided via straps which are attached to the jaws. Each of the tensioning straps can be tightened or loosened individually to allow an even tension to be applied over the whole of the screen.

0009There is becoming an ever increasing need for Pepper's ghost projections in more unusual locations and similarly a great need for larger projection images requiring larger screen sizes (such as those in excess of 5 meters in length). This is placing an increasing burden on the complexity of construction of a projection apparatus capable of projecting a high quality image.

SUMMARY

0010Thus, according to a first aspect of the invention there is provided a polymeric projection screen having a retention member configured, in use, to be in contact with at least one surface of the screen along at least a portion of at least one edge of said screen, characterized in that the retention member is bonded to the screen.

0011The invention therefore provides a simplified arrangement to that described in WO 2005/096095 and other projection screens. For example, a screen width of 12 meters would require approximately 44 holes to be made in the screen. This is not only time consuming but presents a large probability that the screen will be torn, damaged or the overall strength of the screen may be weakened. By contrast, the present invention provides a simplified arrangement wherein the retention members can be simply bonded to the screen at any point without the need for creating holes in the screen and weakening the screen. The resultant screen is therefore more likely to withstand the high tension loads (often as much as 250 kilos of load for every linear meter in width of the foil—thus a 4 m×4 m foil requires 1 000 kilo of break strain to be applied) required to completely eliminate wrinkles without being damaged.

0012It will be appreciated that the retention member may comprise two separate retention members placed either side of the screen such that contact is achieved with both surfaces of the screen. However, in an alternative embodiment, the retention member comprises a single retention member extruded as a substantially U-shaped member such that contact is achieved on both surfaces of the screen. For example, the retention member comprises a channel through which the screen may pass prior to being bonded thereto. In a further alternative embodiment, the retention member comprises a single retention member such that contact is achieved on a single surface of the screen.

0013It will be appreciated that the retention member may be constructed from a variety of materials desirably capable of withstanding the high pressures which will be exerted upon the screen during the tensioning process. In one embodiment, the retention member is constructed from a lightweight metal (e.g. aluminium) or a plastics material. The retention member may be made from a flexible material such that the retention member attached to the screen can be rolled about a cylinder, for example a cylinder having at least a 50 cm diameter and preferably a diameter of between 80 to 100 cm. This is advantageous as the retention member can be attached to the screen at one location and packaged for delivering to another location by rolling the screen and attached retention members about a cylinder. At the delivery location the screen and retention member can be simply unrolled and erected without the need for attaching the retention members and having the necessary tools for attaching the retention members at the delivery location. The retention members may be made of a plastic material that can be extruded. Extruding the retention members is advantageous as very long, for example 100 m long, retention members can be formed such that there is no need to join separate retention members together to form a screen. Joining separate retention members together, such as steel retention members can undesirably result in wrinkles in the screen. In a further embodiment, the retention member is constructed from a plastics material, such as a plastics material (e.g. polyethylene terephthalate; PET).

0014The polymeric projection screen may be constructed from a lightweight material, such as polyester. The use of lightweight material is advantageous as it allows easy manipulation and mounting of the screen in a stage environment.

0015It will be appreciated that the bonding process will typically comprise any means for bonding of the retention member to the screen without requiring holes to be created in the screen. In one embodiment, the bonding will be non-reversible.

0016In one embodiment the bonding comprises a bonding that is suitable for use with polymeric materials, for example the use of welding such as ultrasonic welding.

0017In one embodiment, the bonding may be provided by a single, continuous weld or a series of welds at a plurality of positions. Application of a continuous weld requires the screen to be laid on a flat surface which is not always possible or convenient for large sized screens in venues with limited space. Thus, in a preferred embodiment, the bonding is provided by a series of welds (e.g. spot welds) at a plurality of positions. Spot-welds (e.g. ranging in size from approximately 2-3 mm in diameter or greater, such as approximately 10×15 mm) can be applied by portable welding equipment (e.g. ultrasonic welding equipment). Such equipment is readily available and will typically provide ultrasonic energy at a resonant frequency of between 20 and 40 kHz. This enables simple attachment of a retention member to an edge of the screen.

0018In an alternative embodiment the bonding comprises the use of a chemical agent (e.g. an adhesive). It will be appreciated that the chemical agent may be applied in an analogous manner to that of the ultrasonic welding described hereinbefore (i.e. in either a single, continuous application or a series of applications at a plurality of positions).

0019In a yet further alternative embodiment, the bonding comprises the use of vacuum bonding. Such an embodiment will rely on the use of a material which upon application of pressure to the screen and retention member will create a vacuum bond between the retention member and the screen. Such vacuum bonding provides a simple and strong bonding mechanism. Examples of materials capable of providing such vacuum bonding are currently used in the manufacture of tennis rackets and cricket bats. It will be appreciated that the vacuum bonding may be provided by direct attachment of the retention member to the screen or it may be provided by indirect attachment of the retention member to the screen via the presence of an additional rubberised substrate between the retention member and the screen. This embodiment provides significant advantages over the other forms of bonding provided hereinbefore in that the bonding is reversible and can be re-used. Positioning of the retention members along one edge of the screen in a uniform manner can be a difficult task and the vacuum bonding will allow re-seating to ensure that the retention members are positioned in the optimum position. Furthermore, the bonding properties will remain even when subjected to the influences of heat and moisture. Additionally, the pressure required to form the vacuum bond is very low and therefore the screen is subjected to less tensile pressure and is less likely to be damaged during the bonding process. Although constructed in an entirely different manner to the screen apparatus described in WO 2005/096095, this document describes the presence of an abrasive coating (such as sandpaper) between the screen and the retention member to enhance the grip upon the screen. This abrasive coating causes significant scratching of the screen and in view of the thinness of the screen is very likely to damage the screen and weaken the overall strength of the material. Furthermore, if insufficient force is applied between the retention member and the screen, then the screen will slip and cause undesirable wrinkles in the screen. Thus, the abrasive coating provides a number of disadvantages each of which are solved by the bonding arrangement of the invention (in particular the vacuum bonding embodiment).

0020In an alternative embodiment, the bonding comprises a first retention member composed of a magnetic material in co-operation with a second retention member composed of either a metallic or magnetic material. This magnetic bonding embodiment provides the significant advantage of providing strong bonding by sandwiching the screen between two retention members in addition to providing a reversible bonding process. It will be appreciated that the magnetic material will be any suitable magnet capable of strong attachment to a corresponding metallic or magnetic material. Examples of magnetic materials include iron ore (magnetite or lodestone), cobalt, nickel, gadolinium, dysprosium and rare earth magnets such as samarium (e.g. samarium-cobalt) and neodymium (e.g. neodymium-iron-boron (NIB)) magnets. In one embodiment, the magnetic material is neodymium (e.g. neodymium-iron-boron (NIB)) magnet. In addition to the magnetic retention member embodiment, it is also envisaged that pre-existing metallic retention members can be secured to a screen using magnetic bolts made from a magnetic material as described hereinbefore for the magnetic bonding embodiment. For example, the nut and bolt arrangement may be replaced with a single magnetic bolt which holds the screen firmly in place without the need for tightening a nut to the bolt.

0021In one embodiment, the retention member is located along two opposing sides of the screen. However, it will be appreciated that the retention member need not run the entire length of the edge of the screen. For example, in one embodiment, the length of the retention member may correspond to the length of the screen. In an alternative embodiment, the retention member may comprise a series of shorter lengths along the entire length of the screen. Such embodiments will find applicability in a wide range of varying screen sizes and shapes, in particular non-convention shapes such as triangular, pentagonal, hexagonal or octagonal.

0022Once the retention member has been bonded to the screen as hereinbefore defined, the screen is then tensioned to remove all wrinkles. The tensioning process typically comprises attachment of a plurality of tensioning members to the screen by one end of the tensioning member, with the other end of the tensioning member being attached to a frame or truss member. The tensioning members typically comprise a strap or cord having a ratchet or friction locking buckle. The tensioning members will then be tightened or loosened to result in a wrinkle free screen.

0023The significant advantage of the bonding embodiment of the invention is provided when the screen is tensioned at two opposing sides. If a wrinkle subsequently appears then the bonded retention member described herein may be retrofitted to the screen at any of the remaining sides of the screen in order to simply and effectively remove the wrinkle. For example, pressure could be applied in a different direction to that previously applied which is more likely to remove the wrinkle than simply applying greater pressure in the existing direction. This arrangement of in situ addition of further retention members and tensioning members could not have been possible with the conventional arrangements without complete dismantling of the apparatus. The invention therefore represents a significant advance to current projection arrangements.

0024In one embodiment, the screen has one or more cut-out portions or apertures. These portions will be non-reflective and will typically enable a projector to be positioned such that the image can be beamed through the cut-out portion (or window). This arrangement provides the significant advantage that the “keystone effect” (the creation of elongated or distorted images occurring due to angled projection) is reduced. The cut-out portions may also allow miscellaneous props to be positioned on a live set which may protrude through the screen and create a more realistic 3-dimensional environment. Prior to the invention, these cut-out portions would not have been possible because of the restricted tensioning arrangements. The provision of the in situ addition of individual retention members at any position around the screen provides an effective manner of tensioning a screen to be wrinkle-free even when cut-out portions are present.

0025In one embodiment, the retention members comprise means for attachment of a plurality of tensioning members. In one embodiment, the attachment means comprise a plurality of apertures.

0026Thus, according to a second aspect of the invention there is provided a projection screen having a retention member configured, in use, to be in contact with at least one surface of the screen along at least a portion of at least one edge of said screen, the retention member comprising a plurality of apertures, and a plurality of tensioning members extending through the apertures to apply tension to the screen, wherein a portion of each tensioning member that extends through one of the apertures to contact the retention member is flexible and non-resilient. In this way, forces applied by the tensioning members are substantially in a plane of the screen. In particular, any misalignment of the tensioning member between an attachment point and the plane of the screen that causes twisting of the tensioning member does not result in undue torsion forces being applied to the screen. For example, if the tensioning member comprised a rigid portion that passed through the aperture to contact the retention member, twisting of the tensioning member due to misalignment could result in the rigid portion jamming across the aperture, resulting in the torsion forces being transmitted to the screen. Such torsion forces could create imperfections, such as, wrinkles, in the screen.

0027In this embodiment, a tensioning member may be threaded through the aperture and pressure may be applied to both ends of the tensioning member in the same direction. Such an arrangement provides a simplified attachment mechanism which also has the advantage of being lightweight due to the presence of the apertures. In one embodiment, the apertures are circular, oval or elongated slots. In a preferred embodiment, the apertures are elongated slots.

0028Each tensioning member may comprise a further flexible and non-resilient portion away from a point of contact with the retention member. In this way, the tensioning member can twist between the attachment point and the retention member to compensate for any misalignment.

0029The tensioning members may be straps, such as canvas straps, cord or the like. In an alternative embodiment, the retention members are configured to allow slidable engagement with the tensioning members.

0030Thus, according to a third aspect of the invention there is provided a projection screen having a retention member configured, in use, to be in contact with at least one surfaces of the screen along at least a portion of at least one edge of said screen, characterised in that the retention member is configured to allow slidable engagement with a plurality of tensioning members configured to apply tension to the screen.

0031Such an embodiment provides the advantage that the tensioning members can be moved to any position. This arrangement overcomes the problem of removing a wrinkle which appears between the positions of two fixed tensioning members. In this embodiment of the invention, a slidable tensioning member may be loosened, slid into the position of the wrinkle and then tensioned immediately to remove the wrinkle.

0032According to a further aspect of the invention there is provided a projection screen having a plurality of retention members configured, in use, to be in contact with at least one surfaces of the screen substantially around the periphery of said screen, characterised in that each retention member additionally comprises biasing means configured to bias each retention member away from a neighbouring retention member, the biasing means adjustable to vary the bias applied to the retention member when the screen is in situ.

0033This aspect of the invention provides the significant advantage of a self-tensioning apparatus. For example, the tension provided between each retention member will result in a wrinkle-free screen. The bias can be adjusted to remove/prevent appearance of wrinkles. For example, wrinkles may occur with changes in conditions, such as changes in humidity or temperature and/or due to slackening of the tension of the screen over time. Furthermore, this aspect of the invention does not require a separate frame. The retention members around the periphery of the screen provide a self-supporting screen which neither requires rigging to a frame nor the addition of separate tensioning devices attached to the screen within the frame. This aspect of the invention provides the significant advantage of providing a screen which is both self-supporting and self-tensioning. This arrangement is a significant departure from conventional projection apparatus and optimum results have been achieved with this aspect of the invention when the screen is circular.

0034In one embodiment, the biasing means will comprise a spring or other resilient member. In an alternative embodiment, the biasing means will comprise mechanical means for manually increasing the biasing force exerted between each retention member. Such mechanical means may comprise a threaded nut which is able to extend or retract the distance between each retention member in order to adjust a desired amount of biasing force applied between each retention member.

0035It will be appreciated that the retention member of the self-tensioning aspect of the invention may comprise any suitable retention member (either described hereinbefore or conventionally available). In one embodiment, the retention member comprises two components which hold the screen in place via a clamping action.

0036It will be appreciated that the retention members described herein constitute separate items of commerce from the screen per se and therefore represent additional embodiments of the invention. In particular, the retention member described for the self-tensioning aspect of the invention comprising the biasing means also represents a separate aspect of the invention.

0037In one embodiment, the screen is a foil. In a further embodiment, the screen comprises a partially reflective layer upon at least one surface. In one embodiment, the screen is constructed from the same material as the retention member. In a further embodiment, the screen is constructed from a plastics material (e.g. polyethylene terephthalate; PET). In an additional embodiment the screen is constructed from a biaxially oriented plastic foil.

0038According to a further aspect of the invention there is provided a projection screen comprising biaxially oriented polymeric foil.

0039The biaxial stretching that occurs to the polymeric, such as polyester, extrusion during manufacturing enhances the mechanical properties of stiffness and strength by orienting the molecules in the foil. Of significance is the fact that this stretching process ensures that mechanical properties are roughly similar in the longitudinal direction (along the length of the screen roll) and the transverse direction across the width of the foil. It is this screen property which enables rigging of the screens when tension is generally applied in one direction only e.g. bottom to top or side to side. As the foil has roughly equal properties in both directions the wrinkles are removed fairly easily provided the foil is held stable in the top to bottom orientation as tension is applied.

0040If the foil is not biaxially oriented the wrinkles would be more difficult to remove when tension is applied only in one direction as the foil would tend to narrow across its width. This narrowing across its width (or length if tension is applied only side to side) can to a large extent be stabilized by the use of retention members applied to sandwich the edge region of a foil. The retention members may have bolts that pierce through the foil or have applied to their inner faces abrasive or bonding surfaces that once the retention member is applied, prevent slipping (or contracting) of the foil, preferably, not just in the direction that tension is applied but in all directions. Furthermore the slip control may extend to the far corners of the foil.

0041A further aspect to removing wrinkles in the screens is the need for high tension loads. The screens thus need to have sufficient mechanical properties to resist these loads otherwise the screens will stretch and tear. The molecular stretching process in the manufacture of biaxially oriented polymeric foils results in enhanced mechanical properties which are able to resist the high rigging loads. Screens made from biaxially oriented plastics are also superior to those manufactured from cast or blown film due to these better mechanical properties.

0042The biaxial foil may comprise a silver coating. The biaxial foil may be a contrast foil (a foil having a grey or black tint).

0043According to a further aspect of the invention there is provided an image projection apparatus comprising a light emitting device a frame, and an at least partially transparent screen as hereinbefore defined, the frame being arranged to retain the screen under tension, such that the screen is inclined at an angle with respect to a plane of emission of light from the light emitting device; the screen having a front surface arranged such that light emitted from the display device is reflected therefrom; and

0044the light emitting device being arranged to project an image such that light from the light emitting device impinges upon the screen such that a virtual image is created from light reflected from the screen, the virtual image appearing to be located behind the screen.

0045It will be appreciated that the light emitting device is any light source which is capable of being reflected from an at least partially transparent screen. Examples of light emitting devices include a projector, a liquid crystal display (LCD) screen, a thin-film transistor (TFT) screen, a plasma screen or a light emitting diode (LED) wall (e.g. a high brightness LED wall of variable pitch ranging between 2-30 mm between each LED).

0046The light emitting device can also include objects of stage and set design illuminated by a light that does not necessarily display image processing capabilities.

0047According to a further aspect of the invention, there is provided a method for constructing a projection screen which comprises the steps of:

0048(a) bringing a retention member in contact with at least one surface of the screen along at least a portion of at least one edge of said screen; and

0049(b) bonding the retention member to the screen.

0050In one embodiment, the method additionally comprises the steps of:

0051(c) attaching the at least a portion of at least one edge of said screen to a frame or truss member by one or more tensioning members; and

0052(d) applying tensile force to the one or more tensioning members.

0053The retention member may be made of flexible material and the method may further comprise rolling the projection screen around a cylinder. In this way, the projection screen can be delivered to a required location.

0054According to a further aspect of the invention there is provided a method of constructing a projection screen comprising a) extruding polymeric retention members configured, in use, to be in contact with at least one surface of a screen and b) bonding the retention members to the screen.

0055The method may comprise cutting the extruded retention members to an appropriate length for the screen before bonding the retention members to the screen.

0056It will be appreciated that the features and elements of the invention described hereinbefore for the screen are also applicable to the method described hereinbefore.

0057For example, it will be appreciated that the method of the invention not only finds application in the initial construction of the screen but also in situ tensioning of the screen after construction in order to remove wrinkles during the settling process.

BRIEF DESCRIPTION OF THE DRAWINGS

0058The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

0059<figref idref="DRAWINGS">FIG. 1</figref> shows a front and side view of the ultrasonic bonding embodiment of the invention;

0060<figref idref="DRAWINGS">FIG. 2</figref> shows a front and side view of the ultrasonic bonding embodiment of the invention with the addition of an in situ retention member;

0061<figref idref="DRAWINGS">FIGS. 3 and 4</figref> show a front and side view of the vacuum bonding embodiment of the invention; and

0062<figref idref="DRAWINGS">FIGS. 5 to 7</figref> show differing views of the self-tensioning retention member embodiment of the invention.

0063<figref idref="DRAWINGS">FIG. 8</figref> is a schematic diagram that shows another embodiment of a projection apparatus.

0064<figref idref="DRAWINGS">FIG. 9</figref> is a schematic diagram showing the embodiment of <figref idref="DRAWINGS">FIG. 8</figref> in greater detail.

0065<figref idref="DRAWINGS">FIG. 10</figref> is a schematic diagram showing an embodiment of a control assembly.

0066<figref idref="DRAWINGS">FIG. 11</figref> is a schematic diagram that shows another embodiment of a projection apparatus.

DETAILED DESCRIPTION

0067Referring first to <figref idref="DRAWINGS">FIG. 1</figref>, a projection apparatus shown generally as <b>100</b>, comprises a polymeric projection screen <b>2</b>, retention members <b>3</b>, <b>4</b>, tensioning brackets <b>5</b>, tensioning straps <b>6</b> and a series of ultrasonic spot-welds <b>7</b>. The screen <b>2</b> is shown as a foil and the retention members <b>3</b>, <b>4</b> are each shown as an extruded or moulded plastic (e.g. PET) gripper bar although it will be appreciated that other means of construction could be envisaged.

0068In use, the screen <b>2</b> is inserted into the extruded channel <b>30</b>, <b>40</b> of each of the retention members <b>3</b>, <b>4</b> and then ultrasonically bonded to create the series of spot-welds <b>7</b>. The ultrasonic bonding will be created by a portable ultrasonic welding device comprising an ultrasonic horn backed by a small hand-held anvil. The horn is attached via a cable to a high frequency ultrasonic generator capable of generating ultrasonic energy in the range of 20 to 40 kHz. Each spot weld may typically range from approximately 2 to 3 mm in diameter or greater and takes 1 to 2 seconds to create. The tensioning brackets <b>5</b> are configured to attach to the profiled cross-section of the retention members <b>3</b>, <b>4</b> and tensile force can then be applied to the screen via the tensioning straps <b>6</b>. The tensioning embodiment shown in <figref idref="DRAWINGS">FIG. 1</figref> comprises the sliding engagement embodiment. For example, if wrinkles appear after settling of the screen, a tensioning strap may be loosened, slid to an appropriate position and then re-tensioned to remove the wrinkle. It will be appreciated that the sliding arrangement of the tensioning brackets constitutes an additional inventive feature and finds applicability in other forms of screen and retention member attachment.

0069<figref idref="DRAWINGS">FIG. 2</figref> shows a projection apparatus shown generally as <b>200</b>, comprising a polymeric projection screen <b>2</b>, retention members <b>3</b>, <b>4</b>, tensioning straps <b>6</b>, a series of ultrasonic spot-welds <b>7</b> and a series of elongated slots <b>8</b> within each of the retention members <b>3</b>, <b>4</b>. The screen <b>2</b> is shown as a foil and the retention members <b>3</b>, <b>4</b> are each shown as an extruded or moulded plastic (e.g. PET) gripper bar although it will be appreciated that other means of construction could be envisaged. The tension straps <b>6</b> are flexible and non-resilient such that small misalignment between an attachment point and the plane of the screen <b>2</b> are compensated for by twisting of the tension straps <b>2</b> without applying undue forces to the screen <b>7</b>. In particular, as a portion of the strap <b>6</b> that extends through the apertures <b>8</b> is flexible and resilient the straps do not apply significant lateral forces to the retention member if twisting of the strap <b>6</b> occurs. The forces applied by the tensioning straps <b>6</b> to the screen <b>2</b> are substantially in the plane of the screen <b>2</b>.

0070In use, the screen is bonded to the retention members <b>3</b>, <b>4</b> in an identical manner to that described for the embodiment of <figref idref="DRAWINGS">FIG. 1</figref>. The tensioning arrangement in <figref idref="DRAWINGS">FIG. 2</figref> differs from <figref idref="DRAWINGS">FIG. 1</figref> in that a separate tensioning bracket is not required. Each tensioning strap <b>6</b> passes directly through the aperture <b>8</b> present in the retention members <b>3</b>, <b>4</b>. A further difference between <figref idref="DRAWINGS">FIG. 1</figref> and <figref idref="DRAWINGS">FIG. 2</figref> is the presence of a separate retention member which may be bonded after initial construction of the projection apparatus. In the event that a wrinkle appears following settling of the screen, an additional retention member <b>22</b> may be ultrasonically bonded to the screen <b>2</b> with spot-welds <b>21</b> at the exact position of the screen <b>2</b> which would easily facilitate removal of the wrinkle. The screen can then be tensioned by passing a tensioning strap <b>24</b> through an aperture <b>23</b> present in the retention member <b>22</b> and applying tensile force to the screen <b>2</b> to remove the wrinkle. It will be appreciated that the tensioning arrangement comprising apertures constitutes an additional inventive feature and finds applicability in other forms of screen and retention member attachment.

0071<figref idref="DRAWINGS">FIG. 3</figref> shows a projection apparatus shown generally as <b>300</b>, comprising a projection screen <b>2</b>, retention members <b>3</b><i>a</i>, <b>3</b><i>b</i>, <b>4</b><i>a </i>and <b>4</b><i>b</i>, tensioning brackets <b>5</b>, tensioning straps <b>6</b> and rubberised vacuum forming strips <b>10</b>, <b>11</b>, <b>12</b> and <b>13</b>. The screen <b>2</b> is shown as a foil and the retention members <b>3</b><i>a</i>, <b>3</b><i>b</i>, <b>4</b><i>a </i>and <b>4</b><i>b </i>are each shown as extruded aluminium gripper bars although it will be appreciated that other means of construction could be envisaged.

0072In use, a rubberised vacuum forming strip <b>10</b> is placed against retention member <b>3</b><i>a </i>and a further rubberised vacuum forming strip <b>11</b> is placed against retention member <b>3</b><i>b</i>. One edge of the screen <b>2</b> is then positioned between the retention members <b>3</b><i>a </i>and <b>3</b><i>b </i>(such that the rubberised vacuum forming strips <b>11</b> and <b>12</b> are sandwiched between the retention members and one surface of the screen). Pressure is then applied to the edge of the screen in order to bond the screen <b>2</b> to the retention members <b>3</b><i>a </i>and <b>3</b><i>b </i>via a vacuum bonding process from the vacuum forming strips <b>10</b> and <b>11</b>. The same process is then repeated for an opposing edge of the screen <b>2</b> using rubberised vacuum forming strips <b>12</b> and <b>13</b> and retention members <b>4</b><i>a </i>and <b>4</b><i>b. </i>

0073The tensioning embodiment shown in <figref idref="DRAWINGS">FIG. 3</figref> comprises the sliding engagement embodiment exactly as described in <figref idref="DRAWINGS">FIG. 1</figref>.

0074<figref idref="DRAWINGS">FIG. 4</figref> shows a projection apparatus shown generally as <b>400</b>, comprising a projection screen <b>2</b>, retention members <b>3</b><i>a</i>, <b>3</b><i>b</i>, <b>4</b><i>a </i>and <b>4</b><i>b</i>, tensioning straps <b>6</b>, a series of elongated slots <b>8</b> within each of the retention members <b>3</b><i>a</i>, <b>3</b><i>b</i>, <b>4</b><i>a </i>and <b>4</b><i>b </i>and rubberised vacuum forming strips <b>10</b>, <b>11</b>, <b>12</b> and <b>13</b>. The screen <b>2</b> is shown as a foil and the retention members <b>3</b><i>a</i>, <b>3</b><i>b</i>, <b>4</b><i>a </i>and <b>4</b><i>b </i>are each shown as extruded aluminium gripper bars although it will be appreciated that other means of construction could be envisaged. The bonding process may be performed exactly as described in <figref idref="DRAWINGS">FIG. 3</figref> and the tensioning process may be performed exactly as described in <figref idref="DRAWINGS">FIG. 2</figref>.

0075In an alternative embodiment, the rubberised vacuum forming strips <b>10</b>, <b>11</b>, <b>12</b> and <b>13</b> may be inserted between retention members on conventional projection apparatus (e.g. one which uses the disadvantageous fixing holes with bolts). In this embodiment, the rubberised strips will simply replace the abrasive coating previously used to solve the aforementioned problems. It will be appreciated that in the event that bolts and fixing holes are present, in particular with the slidable tensioning arrangement, that the bolt-heads will be recessed within the retention member to allow sliding of the tensioning bracket.

0076<figref idref="DRAWINGS">FIG. 5</figref> shows the self-tensioning aspect of the invention. The retention member <b>50</b> comprises two components <b>51</b>, <b>52</b> which are configured to sandwich the screen with a clamping action exerted by screw <b>53</b>. C-section couplers <b>61</b> join members <b>51</b> and <b>52</b>. The biasing means <b>54</b> are shown in greater detail in <figref idref="DRAWINGS">FIG. 6</figref> where it can be seen that they comprise two attachment means <b>55</b>, <b>56</b> for attaching the biasing means <b>54</b> to two neighbouring retention members <b>50</b>. The biasing means <b>54</b> also comprise a spring <b>59</b> which is held against a threaded nut <b>60</b>. The biasing means <b>54</b> also comprise fixing holes <b>58</b> for receiving a pin <b>57</b> in order to bias the attachment means <b>55</b> in a fixed position if desired.

0077<figref idref="DRAWINGS">FIG. 7</figref> shows the self-tensioning embodiment attached to a screen <b>2</b>, wherein in use, the two components <b>51</b>, <b>52</b> of each retention member <b>50</b> are placed either side of the screen <b>2</b> and clamped together via tightening and clamped together via tightening of the screw <b>53</b>. Each retention member <b>50</b> will then automatically be biased away from each neighbouring retention member <b>50</b> by the biasing means <b>54</b>. If wrinkles occur in the screen or a greater level of tension is required than exerted naturally by the spring <b>59</b>, then manual adjustment can be made by tightening or loosening the threaded nut <b>60</b>.

0078It will be understood that the self-tensioning aspect of the invention is not limited to circular screens but may be applied to other shaped screens.

0079In one embodiment, the projection screen is a biaxially oriented polyester foil.

0080An embodiment of a projection apparatus that is not configured with a circular screen is depicted in <figref idref="DRAWINGS">FIGS. 8-10</figref>. In <figref idref="DRAWINGS">FIG. 8</figref>, a schematic representation of a projection apparatus <b>100</b> is provided. The projection apparatus incorporates a rectangular support frame <b>102</b>. Note that the support frame is depicted only generally with the exception of the lower frame member <b>104</b>, which is shown in more detail. With this in mind, it is additionally noted that various other shapes and configurations of support frames can be used in other embodiments.

0081As shown in <figref idref="DRAWINGS">FIG. 8</figref>, the support frame defines a projection area <b>106</b>. A polymeric screen <b>108</b> of sheet material that is sized and shaped to span at least a portion of the projection area is mounted to a front of the support frame.

0082<figref idref="DRAWINGS">FIG. 9</figref> depicts a portion of frame member <b>104</b> in greater detail. In particular, the frame member is formed of trusses (e.g., truss <b>110</b>) and define and interior space <b>111</b>) in which various components are positioned and/or by which various components are supported. For instance, representative retention members (e.g., members <b>112</b>, <b>114</b>) are depicted that are operative to contact the polymeric screen to facilitate mounting of the screen to the support frame. In this embodiment, the retention members are positioned along and retain an edge <b>118</b> of the screen and abut the frame member.

0083A tensioning assembly <b>120</b> is operative to apply tension to the screen via the retention members. This is accomplished by the tensioning assembly selectively repositioning the retention members relative to the support frame. In the example depicted in <figref idref="DRAWINGS">FIG. 9</figref>, increasing tension on the screen involves repositioning the retention members by moving the retention members in the direction indicated by arrows A. Note also that the retention members are oriented parallel to a common plane in which the projection area of the screen extends. The retention members apply tension along the common plane to the screen in order to avoid any force concentrations that could otherwise damage the screen in a vicinity of the retention members. Such damage could occur if the retention members were inclined with respect to the common plane.

0084The tensioning assembly incorporates actuators that interconnect the retention members and the support frame. In <figref idref="DRAWINGS">FIG. 9</figref>, two such actuators (i.e., actuators <b>130</b>, <b>132</b>) are depicted. Each of the actuators in this embodiment includes a piston (e.g., piston <b>134</b>), which is anchored to the support frame on one end and attached to a coupler on the other end. Each coupler (e.g., coupler <b>136</b>) mechanically links the corresponding retention member and piston. Note that, in this embodiment, each coupler is a flexible coupler (e.g., a strap) that redirects force generated by the piston and transfers that redirected force to the associated retention member so that movement of the piston repositions the retention member relative to the support frame. For instance, movement of the piston in a generally lateral direction is redirected to movement of an end of the coupler in a generally vertical direction. Also note that the force is generated responsive to the piston moving between an extended position and a contracted position.

0085In the embodiment of <figref idref="DRAWINGS">FIG. 9</figref>, retention member <b>112</b> includes a first elongate member <b>142</b>, a second elongate member <b>144</b> and a screen-receiving channel <b>146</b> defined between the members <b>142</b>, <b>144</b>. Each of the members (e.g., member <b>144</b>) also includes a projection area-facing side (e.g., side <b>148</b>), an outward-facing side (e.g., side <b>149</b>), a screen-facing edge (e.g., edge <b>150</b>) and an outward-facing edge (e.g., <b>151</b>). In this embodiment, each of the screen-facing edges includes a protruding lip (e.g., lip <b>152</b>) that extends along the length of the member.

0086A gasket (e.g., gasket <b>154</b>) is positioned within the corresponding screen-receiving channel and is retained by the protruding lip. So configured, the gasket is operative to contact the edge of the polymeric screen, which is positioned within the screen-receiving channel. Thus, the edge of the polymeric screen is positioned between and contacted by opposing contact surfaces of the gaskets.

0087In some embodiments, the gaskets can be formed of cork, such as in the form of strips of cork positioned within the channels. Notably, the gaskets can provide cushioning for preventing damage to the screen and, depending on the particular materials used, may form vacuum seals (e.g., intermittent seals) along the contact surface of the gasket.

0088Also shown in <figref idref="DRAWINGS">FIG. 9</figref> are control lines (e.g., control line <b>158</b>) that provide inputs to the actuators. In this embodiment, the control lines are configured as pneumatic conduit for routing pressurized gas to the pistons for causing the pistons to move between the extended and retracted positions. In other embodiments, another control medium could be used.

0089Referring to <figref idref="DRAWINGS">FIG. 10</figref>, a representative embodiment of a control assembly that interacts with a tensioning assembly is schematically depicted. As shown in <figref idref="DRAWINGS">FIG. 10</figref>, control assembly <b>160</b> includes a pressure source <b>162</b> (e.g., a pressurized air source), a control component <b>164</b>, a primary manifold <b>166</b>, multiple secondary or subset manifolds (e.g., manifold <b>168</b>) and associated control lines (e.g., line <b>158</b>), with multiple pistons (e.g., piston <b>134</b>) communicating with each of the subset manifolds. The pressure source, control component, manifolds, control lines and pistons are positioned within interior space <b>111</b> defined by the frame member <b>104</b>. Note also that various other numbers and configurations can be used in other embodiments. For example, in some embodiments, a subset manifold may not be used.

0090The manifold communicates with the pressure source and is operative to distribute pressure from the pressure source responsive to control inputs from the control component. In some embodiments, the control component may be as simple as an interposed valve although various other configurations could be used. The primary manifold distributes the pressure to one or more of the subset manifolds for further distribution to the actuators. More specifically, in this embodiment, the actuators incorporate pneumatic pistons to which the pressurized gas is routed so that the pistons reposition corresponding retention members for tensioning the screen.

0091In this regard, an embodiment of a method for providing a projection screen for displaying images of a light emitting device broadly includes the following steps: providing a projection screen formed of sheet material; retaining an edge of the projection screen; and placing the projection screen under tension via the edge of the projection screen using pressure from a pressure source to reduce wrinkles in the projection screen. As mentioned before, in some embodiments, in retaining the edge of the projection screen, a gasket is used to contact the screen such as when clamping the edge of the screen between opposing gaskets. Note also that, in some embodiments, the projection screen is placed under tension only along a common plane in which the screen is located.

0092<figref idref="DRAWINGS">FIG. 11</figref> is a schematic diagram that shows another embodiment of a projection apparatus. As shown in <figref idref="DRAWINGS">FIG. 11</figref>, projection apparatus <b>200</b> incorporates a support frame <b>202</b>. Note, much like in <figref idref="DRAWINGS">FIG. 8</figref>, the support frame in <figref idref="DRAWINGS">FIG. 11</figref> is depicted only generally. Notably, however, the support frame defines a projection area <b>206</b> across which a polymeric screen <b>208</b> of sheet material is mounted.

0093In contrast to the embodiment depicted in <figref idref="DRAWINGS">FIG. 8</figref>, projection apparatus <b>200</b> incorporates opposing sets of retention members. Specifically, sets of retention members are oriented along all of the edges of the screen, with each set extending along substantially the entire length of the corresponding edge. In such an embodiment, tensioning assemblies could be used for directly tensioning each edge of the screen. Alternatively, with respect to each pair of opposing sets of retention members (e.g., opposing sets of members <b>210</b>, <b>212</b>), only one of the sets may include tensioning assemblies. In such an embodiment, the set of members that is not provisioned with tensioning assemblies would likely be held stationary with respect to the support frame so that movement of the other set of members applies tension to the screen.

0094Also depicted in <figref idref="DRAWINGS">FIG. 11</figref> (in phantom lines) is a portion of a trim kit or skirt <b>214</b>. The skirt can be formed of various materials (e.g., cloth) and is primarily used as a decorative feature for concealing various components from viewers located in front of the screen.